Steam distilling pyrolysis gasoline

ABSTRACT

A method of separating dripolene from entrained higher boiling hydrocarbons using a steam stripper is disclosed. The stripper is operated without sufficient preheating of feed, with partial condensation of the steam, and at about 200* to 235* F.

United States Patent Grosboll [451 Jan. 25, 1972 [54] STEAM DISTILLING PYROLYSIS GASOLINE [72] Inventor: Martin P. Grosboll, Homewood, Ill.

[73] Assignee: Atlantic Richiield Company, New York,

[22] Filed: Mar.11,1969

[21] Appl.No.: 806,306

[52] US. Cl ..208/363, 208/102 [51] [58] 208/363, 102, 255,48

Primary ExaminerHerbert Levine AttorneyJ0hn W. Behringer, Eugene L. Bernard, Martin .1. Brown, James N. Dresser, W. Brown Morton, Jr., John T. Roberts, Malcolm L. Sutherland and Morton, Bernard, Brown, Roberts & Sutherland s7 ABSTRACT A method of separating dripolene from entrained higher boilin g hydrocarbons using a steam stripper is disclosed. The stripper is operated without sufficient preheating of feed, with partial condensation of the steam, and at about 200 to 235 F.

3 Claims, N0 Drawings STEAM DISTILLING PYROLYSIS GASOLINE The present invention is directed to the separation of hydrocarbon fractions. More particularly, the invention is directed to the removal of higher boiling hydrocarbons, such as lubricants from a byproduct obtained in the pyrolysis of hydrocarbons such as ethane, propane and naphtha to produce ethylene.

The pyrolysis byproduct boiling up to and including the gasoline range is known in the art as dripolene or pyrolysis gasoline and has commercial value when boiling within the range of about 95 to 400 F. However, for greater value dripolene must have an end boiling point of about 400 F. or less. Higher boiling hydrocarbons, such as found in lube oil, when mixed with dripolene will raise the end boiling point above 400 F. Lube oil becomes mixed with the dripolene in the process gas compressors when lube oil is injected to prevent fouling of the compressor internals. Thus an effective method of separating the dripolene and higher boiling oils is of value. Systems such as flashing the dripolene are not effective since at low temperatures the recovery is poor and the dripolene fraction tends to polymerize at higher temperatures due to the presence of materials, such as diolefins and styrene.

The present invention, however, avoids such problems by steam stripping the dripolene-higher boiling oil mixture with condensation of at least part of the steam. Steam stripping lowers the hydrocarbon partial pressure so that the separation may be effected at a temperature where polymerization is reduced. By purposely condensing part of the steam, e.g., at least about 5, or even at least about weight percent say up to about 50 weight percent, introduced into the column used in the method of this invention, no feed preheating is required thereby eliminating a potential fouling problem through polymerization. Also, by condensing part of the steam in the stripper, the total steam added is considerably reduced over that which would be required if the heat for dripolene vaporization were to come solely from the superheat of the steam. The condensed steam can be easily separated from the unvaporized oil bottoms and uncondensed overhead steam is also easily separated from the distilled dripolene.

In general the process of this invention is characterized by feeding the dripolene-higher boiling oil mixture essentially as a liquid to a stripping column where steam is fed directly into contact with the mixture. The stripping column may be of any vapor-liquid contacting type, as, for example, a packed column or a tray column. Where tray columns are utilized, it is preferable to introduce the steam immediately below the trays. A portion of the steam is condensed to provide heat for vaporization and driving off the dripolene which is taken overhead from the stripper, cooled, and condensed. Overhead steam is also separated in the cooling-condensing step to produce a saleable dripolene product. Condensed steam and unvaporized oil can be removed from the bottom of the column via separate line.

More specifically, the dripolene-higher boiling oil mixture is fed directly into the steam stripper, without sufficient preheating, that is, at a temperature of up to about 190 F., e.g., from about ambient to about 190 F., preferably about 140 to 180 F. and even more preferably about 165 F., and contacted with steam in the column at a temperature sufficient to strip substantially all of the dripolene, but without substantial polymerization, e.g., about 200 to 235 F., preferably about 215 to 230 F., and at reduced, atmospheric, or slightly higher pressures, e.g., up to about 30 p.s.i.g., preferably up to about p.s.i.g. The temperature difference between the dripolene-higher boiling oil feed and the steam can be small as long as sufficient heat is supplied by the steam to cause vaporization of the dripolene. The steam can conveniently be introduced into the stripping column at up to about 150 or more p.s.i.g., e.g., at, for instance, temperatures of up to about 370 F.

The overhead fraction, consisting of uncondensed steam and dripolene is cooled and condensed, e.g., at about 90 to 130 F., preferably at about to l 10 F., and at atmospheric pressure. These condensed materials separate in a tank from which the waste water and dripolene product are withdrawn by separate lines. Condensed steam and a material being substantially mixed higher boiling oils form two phases in the bottom of the stripper and can be withdrawn via separate lines from the bottom of the column.

The invention is further illustrated by the following example.

Sixteen and one half barrels per hour at 165 F. of higher boiling oil-containing dripolene is contacted with 3,938 lbs/hr. of p.s.i.g. steam in a six (6) tray (20-inch spacing) vapor-liquid contacting column which is operated at 218 F. at the top and 228 F. at the bottom. The steam enters the column just below the bottom tray. The overhead is cooled and condensed to 105 F. at atmospheric pressure and 11.5 bbls./hr. of dripolene product are separated as the upper phase in the condenser, water being removed as the lower phase. Five barrels per hour of substantially higher boiling oil are drawn from the upper liquid phase in the bottom of the column while water is taken from the lower phase as bottoms. The lube oil draw is taken below the steam inlet line.

The following table indicates the substantially complete separation of high-boiling lube oils from the dripolene product by the method of this invention.

(1) Steam to stripper (lb./hr.)

It is claimed:

1. A method of separating pyrolysis gasoline from higher boiling hydrocarbons contained therein which comprises charging said pyrolysis gasoline in the liquid phase and at a temperature of up to about 190 F. to a stripping column, charging steam to said column to contact said pyrolysis gasoline containing higher boiling hydrocarbons and condensing at least about 5 weight percent of the steam charged to said column while maintaining said pyrolysis gasoline in the column at a temperature of about 200 to 235 F., said condensed steam and said higher boiling hydrocarbons in liquid phase forming in the lower portion of said column, withdrawing steam and pyrolysis gasoline as overhead from the column, and separately withdrawing said condensed steam and said higher boiling hydrocarbons from the lower portion of the column.

2. The method of claim 1 wherein the temperature of the pyrolysis gasoline charged to the column is about to F. and the temperature of the pyrolysis gasoline in the column is about 215 to 230 F.

3. The method of claim 2 in which about 10 to 50 weight percent of the steam charged to the column is condensed therein. 

2. The method of claim 1 wherein the temperature of the pyrolysis gasoline charged to the column is about 140* to 180* F. and the temperature of the pyrolysis gasoline in the column is about 215* to 230* F.
 3. The method of claim 2 in which about 10 to 50 weight percent of the steam charged to the column is condensed therein. 